Re: [patch] change futex_wait() to hrtimers

[Ingo Molnar <mingo@elte.hu>]

* Andi Kleen <andi@firstfloor.org> wrote:

> On Mon, Mar 12, 2007 at 12:00:20PM +0100, Thomas Gleixner wrote:
> > On Mon, 2007-03-12 at 12:27 +0100, Andi Kleen wrote:
> > > Ingo Molnar <mingo@elte.hu> writes:
> > > > 
> > > > the only correct approach is the use of hrtimers, and a patch exists for 
> > > > that - see below. This has been included in -rt for quite some time.
> > > 
> > > But isn't that bad for power management? You'll likely get more
> > > idle wakeups, won't you?
> > 
> > Why so ? It comes more precise, but only once.
> 
> When it's clustered around the jiffies interval then wakeups from 
> multiple processes will be somewhat batched. With a precise wakeup 
> you'll get wakeups all over the jiffies period, won't you?

if HIGH_RES_TIMERS is disabled then that is what happens. But frankly, 
most futex waits are without timeouts - if an application cares about 
micro-effects like that then you are much better off not using a 
per-futex timeout anyway.

	Ingo